Compression molded plastic closures have found very widespread acceptance in the marketplace, with such closures being particularly suited for use on carbonated beverages, as well as other applications requiring the desirable strength and sealing characteristics which such closures can provide. Additionally, these types of closures can be readily configured to provide tamper-indication, thus assuring consumers of the desired product quality.
U.S. Pat. No. 4,378,893, No. 4,407,422, No. 4,418,828, and No. 4,978,017, all hereby incorporated by reference, illustrate plastic closure constructions, including closures which can be configured for tamper-indication, which can be efficiently and economically formed by compression molding. U.S. Pat. No. 4,343,754, No. 4,497,765, No. 5,554,327, No. 5,670,100, and No. 5,866,177, all hereby incorporated by reference, disclose methods and apparatus by which plastic closures can be formed by compression molding.
For typical applications, a compression molded closure includes a retention element, typically in the form of a helical thread formation, on an inside surface of a skirt portion of the closure. A male mold of the compression molding tooling, sometimes referred to as a forming pin, includes an outer mold surface which is suitably configured for formation of the closure thread formation. In order to facilitate high-speed manufacture of such closures, it has typically been the practice to mechanically “strip” the molded plastic closure from the forming pin, without any relative rotation for “unthreading” the closure from the forming pin. Mechanical stripping of the interference fit between the molded closure and the forming pin requires that the skirt portion of the closure be outwardly deformed as the closure threads are urged out of the grooves or other features of the forming pin within which they are molded.
Experience has shown that deformation of the thread formation which can occur attendant to this stripping action generally acts to limit the speeds with which plastic closures can be formed. While typical rotary compression molding machines include water cooling passages within the mold tooling components, operational speeds are typically limited by the time required for the molded thread formation to become sufficiently solid as to permit the mechanical stripping of each closure from its respective forming pin, without unacceptable deformation of the thread formation or other portions of the closure.
Heretofore, efforts have been made to facilitate this mechanical stripping of a threaded plastic closure from an associated male mold tooling. Use of compressed gas, directed into a molded plastic closure during removal from associated tooling, has been practiced in connection with injection molding of closures. Efforts have also been made to incorporate such air-ejection arrangements in compression molding equipment, such as exemplified by U.S. Pat. No. 5,786,079, hereby incorporated by reference, and published PCT patent application No. WO 01/32390, hereby incorporated by reference. However, these previously known arrangements have undesirably increased the complexity of tooling, and in one construction, required the provision of an air passage which generally tends to reduce the sizes of coolant passages within the tooling. Such arrangements have also been generally limited in the size of passageways provided for direction of air into a molded closure, and have been configured in a way which can undesirably result in thin metal portions of tooling, detracting from durability.
The present invention is directed to an improved apparatus for compression molding of plastic closures, and method of operation, which facilitates high-speed closure manufacture by introduction of compressed gas, air, typically into a molded closure during its removal from an associated male mold forming pin, with the system desirably configured to maintain the integrity of the associated tooling, and permitting cost-effective use in compression molding equipment.